Am i the only one who feels so uncomfy telling someone to KYS?

Like the last time I did that was when a troller tried to like impersonate my dead bf even which was like fucked up and I hated that. I didn't wanna say that but I was so pissed at the thought of someone pretending to be him and harassing his friends. Anyways, it's just like so easy for some ppl to tell that to someone for like an opinion on something or they're trying to educate someone. Istg i got told to "Kys" few times for sometimes venting here which it doesn't even harm you, so why are you so pissed? I get jokes like with your friends or something but being half serious about it, or anything else outside of friendly manner is disgusting to me. Only time I'd let that excuse is that if this person was like supporting rape or is a pedophile. Like they're actually so horrible as a person, even though I can hate someone so much I don't even say it. I mean if you're one of the ppl who told my bf to kill himself, I'd probably do it out of anger but other than that? I can't say it... Even as a joke sometimes i hesitate to do so. The last time was over 5 months ago and it was like someone being hella disrespectful to the dead and I FELT BAD. Anyways why is this so normalised? Why do ppl resort to death threats or suicide threats bec of something so small that DOESN'T even harm them. That "Kys" is harmful cus u don't know what this person's going through.